1. Field of the Invention
The present invention relates to a shutter for a camera and, more particularly, it relates to a shutter including a plurality of successively overlapping light shielding blades and a plurality of driving arms for holding and driving said light shielding blades to produce linked parallel movements of said light shielding blades.
2. Description of the Related Art
Heretofore, the light shielding blade of the shutter of this kind has been made of common steel plate or stainless steel plate, in order to assure high mechanical strength of the shutter blade, and an arm for holding and driving such a heavy shutter blade requires higher strength. As the result, it has been a common technical knowledge that a limit shutter speed is 1/1000 sec at maximum.
However, in order to assure synchronism of exposures at various portions of an object and to enlarge a photographing area, it has been required to move a shutter blade at a higher speed.
As a measure of increasing the speed of the shutter blade, it has been proposed to decrease the weight of the blade. Such proposals are disclosed for example, in U.S. Pat. Nos. 4,529,285 (patented: July 16, 1985), 4,298,265 (patented: Nov., 1981), 4,486,084 (patented: Dec. 4, 1984) and 4,401,380 (patented: Aug. 30, 1983). It has been also proposed to use a shutter blade of titanum plate instead of steel plate, forming depressions thereon by etching process and forming a surface hardened layer by nitriding treatment or the like, thereby decreasing the weight while increasing the strength of the shutter blade (for example, see Japanese Laid-Open Utility Model Application No. 54-173742, Japanese Laid-Open Patent Application No. 55-161223). It has been further proposed to use a plate of high-strength, anodized aluminum alloy (for example, see Japanese Laid-Open Patent Application No. 57-24925). These proposals enable to increase the shutter speed to 1/2000 sec., 1/4000 sec. or more.
According to the construction of the blade material now used, however, further increase of the blade speed to attain higher shutter speeds, such as 1/8000 sec., is very difficult by only decreasing the weight of the blades and it may be required to increase the blade winding-up energy by increasing the spring force for driving the blade or to increase the strength of the braking mechanism.
Under such circumstances, it has been also proposed to reduce the weight of the blade holding and driving arms also. In such viewpoint, it is possible to reduce the weight of the arm by making the arm of titanium plate, thinning said plate by etching process and then increasing the strength by nitriding process (see Japanese Laid-Open Patent Application No. 54-63823). Such a measure, however, tends to considerably increase the manufacturing cost of the shutter and it requires a large equipment to effect processing of factory wastes. Furthermore, the measure of reducing the weight of the arm only by thinning the arm gives rise to such disadvantages as the decrease of strength of the arm, the increase of wearing of the hole portion of pivotally supporting the blade and the like.